Sticking with jerk (3)
I believe the answer is:
tic
'jerk' is the definition.
(jerking movement by the body)
'sticking with' is the wordplay.
'with' says the answer is hidden in the clue.
'TIC' can be found hidden inside 'sticking'.
(Other definitions for tic that I've seen before include "Convulsion" , "Involuntary twitch" , "Involuntary muscular spasm" , "Muscle twitch" , "Nervous movement" .)